Field of the Invention
The present invention relates to an image output apparatus and an image output method.
Priority is claimed on Japanese Patent Application No. 2013-215739, filed Oct. 16, 2013, the content of which is incorporated herein by reference.
Description of Related Art
In an imaging apparatus such as a camera for still images or a camera for moving images, a configuration causing a captured photographic image to be displayed on a display device such as a LCD (liquid crystal display) installed on the imaging apparatus has been known.
In the imaging apparatus having such a configuration, when a photographic image is displayed on the display device, an OSD (on-screen display) image such as a character image is displayed to be superimposed on the photographic image as well.
In such an imaging apparatus, generally, an image output apparatus is a circuit that is built in in a system LSI or an image processing LSI in the imaging apparatus. The image output apparatus generates a display image. The image output apparatus generates a synthetic display image synthesized by superimposing a plurality of input images such as a photographic image and an OSD image (see FIG. 6), and outputs the generated synthetic image to be displayed on the display device. At this time, the image output apparatus generates and outputs a synthetic image periodically according to a period by which a frame rate of the display device on which an image being displayed is updated, regardless of whether an image to be displayed on the display device has been updated.
Further, in the imaging apparatus, the image output apparatus generally acquires each input image used for generation of a synthetic image from an external storage area such as a memory similarly connected to a direct memory access (DMA) bus via the DMA bus to which the system LSI or the image processing LSI including the image output apparatus is connected, through DMA transfer. For this reason, when the number of input images used for generation of a single synthetic image increases, during each period by which the frame rate of the display device is updated, an amount of image data to be processed (transferred) through the DMA transfer increases, and thus there is a problem in that power consumption of the image output apparatus increases.
In this regard, as a technique of reducing the power consumption of the image output apparatus, there is, for example, a technique disclosed in JP 2006-003876A. In the technique disclosed in JP 2006-003876A, an image output apparatus outputs a synthetic image generated by causing a plurality of input images acquired from an external storage area to be superimposed on one another to a display device, and stores the generated synthetic image in an external storage area which is different from that of the input image. Further, in the technique disclosed in JP 2006-003876A, when not all input images are updated within a certain period of time, instead of acquiring the input images used for generation of the synthetic image, the image output apparatus acquires the stored synthetic image from the external storage area, and outputs the acquired synthetic image to the display device. Further, in the technique disclosed in JP 2006-003876A, when any one input image is updated within a certain period of time, the image output apparatus acquires all input images used for generation of the synthetic image from the external storage area, outputs a newly generated synthetic image to the display device, and causes the generated new synthetic image to be stored in an external storage area (different from that of the input image).
As described above, in the technique disclosed in JP 2006-003876A, based on whether or not the input image used for generation of the synthetic image has been updated within a certain period of time, an image to be acquired from the external storage area is changed during each period by which the frame rate of the display device is updated, and thus the power consumption of the image output apparatus is reduced when the image to be displayed on the display device has not been updated. More specifically, when no input image is updated, an operation of acquiring the already generated synthetic image from the external storage area is performed, and thus an amount of image data to be transferred through the DMA transfer is reduced to be smaller than when all input images are acquired from the external storage area, and the power consumption of the image output apparatus is reduced. Furthermore, in the technique disclosed in JP 2006-003876A, operations of components other than a circuit used to acquire a synthetic image are stopped, and thus the power consumption of the image output apparatus can be further reduced.
Regarding displaying the image on the display device, there are a situation that an input image is not updated by each frame, that is, a situation that update frequency of the input image is low, and a situation that the input image is updated by each frame, that is, a situation that update frequency of the input image is high. In such a situation that update frequency of the input image is low, for example, there are a situation of displaying a confirmation image to check a captured still image, and a situation of displaying a recorded still image stored in recording medium such as a memory card. As the situation that the update frequency of the input images is high, for example, there is a situation of checking a subject in a still image or a moving image, that is, a situation of displaying a live-view image (through-the-lens image). Therefore, it is necessary that the image output apparatus does not only generate a synthetic image based on the input images whose update frequency is low, but also generates a synthetic image based on the input images including more than one input image whose update frequency is high, such as the live-view images that are always updated, during each period at which the frame-rate of the display device is updated.